Chlorofluorocarbons (CFC's) were once widely used solvents for precision cleaning of parts and components due to their superior physical and chemical properties, especially their solvency for contaminating materials such as oils, greases, resin fluxes, particulates, and other contaminates. One solvent commonly used in many applications was CFC-11 (trichlorofluoromethane). CFC-11 has many favorable characteristics such as low toxicity, non-flammability and stability.
The use of CFC-11, however, has become restricted due to its ability to react and deplete atmospheric ozone. By the mid-1980s, problems regarding the ozone became apparent, and the primary culprits were identified as certain halogenated hydrocarbons including CFC-11. Thus, nontoxic and non-ozone depleting replacement solvents became a priority for cleaning applications. Various CFC-11 substitutes have emerged but they do not clean as well, are flammable, or have other drawbacks.
Many factors are important when selecting CFC second-generation replacement solvents. Some of the critical performance properties of CFC replacements include: cleaning effectiveness or solvency, volatility (e.g., boiling point), compatibility with materials to be cleaned (e.g. metals, elastomers and systems), toxicity, environmental persistence, flammability, cost and availability.
The purpose of flushing line sets in HVAC/R systems is to remove acid, moisture, contaminates and oil from the line-sets that are being used after a system failure or when the indoor and outdoor components of the air conditioner are being replaced and the line-set is being reused. A contaminated refrigeration or air conditioning system may have drastically reduced life resulting from compressor failure, for example. The materials and contaminants in these systems differ from other applications and therefore solvents must be optimized accordingly. For example, a flushing solvent must be compatible with the elastomers and metals in typical systems, while at the same time have the solvency properties to remove oils, acids, moisture and decomposition products of the oils and refrigerants. While many solvents can dissolve oil, it is far more important to also remove acid and moisture in HVAC/R systems.
In spite of the fact that the most critical performance metrics for a refrigeration system flush are moisture and acid absorption capacities, typical refrigeration flushes only remove oil. A common EPA SNAP-approved flushing solvent, trans-dichloroethylene (t-DCE), is miscible with mineral oil. Mineral oil is a typical contaminant in an HVAC/R system when the system is converted from R-22 to a newer refrigerant such as R-410A. While t-DCE will strongly absorb mineral oil, it has low absorption capacities for moisture and strong acids, the latter being present in large numbers in a system after a compressor burnout. Any vapor compression refrigeration or air conditioning system flushing agent should also be nonflammable when dispensed in an aerosol form as determined by ASTM D3065-01. However, t-DCE itself is flammable, and therefore requires non-flammable co-solvents and/or propellants to pass this flammability test.
Hydrofluoroethers have recently gained traction as working fluids for a number of applications due to their low global warming potential (GWP) and zero ozone depletion potential (ODP). They can also be engineered to be nonflammable and nontoxic. Specifically, methoxytridecafluoroheptene isomers (MFHs) have been shown to be miscible with t-DCE so that they can be used as blending agents in solvent applications, as taught in U.S. Pat. No. 8,410,039. They also have low GWP and zero ODP. The addition of MFHs to t-DCE can be made to result in an azeotropic or near azeotropic mixture that does not have a measurable closed cup flash point (e.g., Chemours Vertrel™/Opteon™ Sion™). The acid and moisture absorption capacities of the resulting binary t-DCE/MFHs mixtures are, however, still relatively poor.
Hydrofluorocarbons (HFCs) can also be used to inhibit the flammability of t-DCE. One particular HFC for inhibiting flammability is 1,1,1,3,3,-pentafluorobutane (HFC-365mfc). A mixture of t-DCE and HFC-365mfc is disclosed in U.S. Pat. No. 5,478,492 where compositions were at least 56% by weight of HFC-365mfc. Methyl nonafluorobutyl ether isomers (e.g., Novec™ 7100 by 3M) can also be added to t-DCE/HFC-365mfc mixtures to further refine the flammability and performance trade-offs as taught in U.S. Pat. No. 6,951,835. EnSolv® NEXT by Enviro Tech is one such solvent mixture of t-DCE, HFC-365mfc and methyl nonafluoroisobutyl ether (MFBE) where the major component is t-DCE. The published Safety Data Sheet (SDS) indicates ranges of 70-90 wt % t-DCE and 15-25 wt % HFC-365mfc and 1-10 wt % MFBE in EnSolv® NEXT.
The solvencies of HFC-365mfc and HFEs are generally poorer than t-DCE due to their lower Kauri-Butanol (KB) values (12 and 10 for HFC-365mfc and MFBE, respectively, compared to 117 for t-DCE). However, HFC-365mfc (F/H mole ratio=1) has a better KB value compared to other inerting HFCs with higher F/H mole ratios (e.g. greater than 1.6) such as HFC-43-10mee (KB=9). Therefore, HFC-365mfc is more desirable than HFC-43-10mee in terms of cleaning capacity. HFC-43-10mee is taught as an inerting solvent in U.S. Pat. No. 6,852,684 at concentrations of 20-45 wt % excluding propellant. A higher KB value generally correlates to a better ability to dissolve hydrocarbon oils and greases. Therefore, higher concentrations of t-DCE than HFC or HFE inerting agents are desirable in cleaning solvents. The formulas taught by U.S. Pat. No. 6,852,684 are limited to 55-75 wt % t-DCE. It is critical, but heretofore unattainable due to flammability issues, to further increase the amount of t-DCE and/or moisture and acid removal additives in the formula. However, I have discovered a means to significantly increase the KB value of the mixture to provide superior solvency compared to the inerting additives.
A drawback of HFC-365mfc relative to the inerting agents taught in U.S. Pat. No. 6,852,684 however, is less effective flame suppression, itself having a flash point of −27° C. It is known to form non-flammable mixtures with t-DCE but the flammability characteristics are more complicated than with HFC-43-10mee. EnSolv® NEXT uses a small amount of MFBE to further inert the mixture of t-DCE and HFC-365mfc. Nevertheless, additional flame mitigation is highly desired for use in aerosol HVAC flushing compositions.
As shown in examples presented below, the addition of the MFHs and/or HFC-365mfc/MFBE only modestly increases moisture and acid absorption capacities. I have recognized that another way to improve the moisture and acid adsorption is clearly needed. It is important to understand that vapor compression air conditioning, refrigerant and similar systems are sealed, pressurized and relatively-clean systems and, while the removal of contaminants and lubricants is important, it is equally as critical to remove residual acid and moisture, since small amounts of the old oil can be tolerated in the new system but moisture and acid can quickly lead to system failure.
Acetone and t-butyl acetate can be used as flushing additives to improve water and acid absorption as taught in U.S. Pat. No. 8,557,759. However, these additives are not as effective as n-propanol as will be shown in the following examples. Acetone is also more expensive than many alcohols, including n-propanol. U.S. Pat. No. 6,852,684 teaches the use of numerous non-azeotropic organic additives with t-DCE to modify solvent properties including alcohols, ketones, esters, siloxanes and ethers. However, they do not suggest using or show data for HFC-365mfc or MFHs as inerting solvents or n-propanol as a property modification solvent for t-DCE. Additionally, all of their flammability test data with ASTM D-3065 appears to have been obtained with 20 wt % propellant in an aerosol formula without ever suggesting aerosols with higher propellant loadings. Table 1 Summary beginning on line 15 of column 9 of U.S. Pat. No. 6,852,684 teaches the minimum amount of inerting solvent required in an aerosol with 20 wt % R-134a propellant in order to obtain flame projection less than 18″ during ASTM D-3065. This table includes ranges of inerting solvents from 24-42 wt % on a propellant-free basis which corresponds to wt % ratios of inerting solvent/property modification solvent ranging from 1.8-3.2. A key element of my invention is enabling the use of lower inerting solvent/property modification solvent wt % ratios less than 1.5 by including additional propellant beyond 20 wt %. This is highly beneficial because it enables additional productive flammable solvent (t-DCE and/or property modification solvent) to be used in the formula while remaining non-flammable by ASTM D-3065.
Power Flush by Atlantic Chemical & Equipment Company includes 1-9 wt % ethanol in the aerosolized product. However, this formula only includes 50-60 wt % t-DCE. As stated earlier, formulas with more t-DCE are desirable for oil and contaminant cleaning. This formula also uses HFC-43-10mee which is inferior to HFC-365mfc and many HFE inerting agents in terms of cleaning capacity. This formula uses 16-24 wt % HFC-43-10mee, which results in a minimum wt % ratio of inerting solvent/property modification solvent (i.e. HFC-43-10mee/ethanol) greater than 1.7. Once again my invention, enables the more desirable use of lower inerting solvent/property modification solvent wt % ratios of less than 1.5 while remaining non-flammable by ASTM D-3065.
A DiversiTech Product Development document lists acetone as the “moisture scavenger” in Pro-Flush™ and ethyl alcohol as the “moisture scavenger” in a Nu-Calgon Corp. product Rx-11. The current formulation of Rx-11 on the market is not believed to contain any alcohol based on more recent Nu-Calgon Safety Data Sheets. Previous tests with an earlier formulation containing alcohol were shown to be flammable which may explain why the alcohol was removed.
I discovered a formulation that has excellent acid, moisture and oil cleaning capabilities and yet remains a non-flammable aerosol. That is, I have been able to maximize the percentage of flammable t-DCE in the formulation while also adding another flammable component n-propanol to dramatically improve the removal of acid and water which, as stated earlier, are critically important impurities to be removed. While the prior art has used ethanol for water removal in other commercial flushes, I have found that although ethanol performs similarly to n-propanol for acid and moisture removal in solution with t-DCE and inerting co-solvents, n-propanol is superior to ethanol in my formulation because it has a higher closed cup flash point (72° F. for n-propanol, 57° F. for ethanol) but similar performance. Because n-propanol is less flammable than ethanol, more n-propanol or t-DCE can be included in the same formula while remaining non-flammable.